1. Field of the Invention
The present invention relates to an optical printer with a spatial light modulator constituted of a micromirror device having a large number of very small mirrors with variable reflecting direction.
2. Background Arts
Optical printers print pictures, including characters and drawings, on photosensitive materials, such as photographic paper. Of the optical printers, color photographic printers that project an optical image of a picture frame from negative photographic film onto photographic paper have been widely used. Recently, digital optical printers have been developed and used in practice that drive a display device in accordance with digital image data to print a picture by projecting printing light beams or an optical image from the display device onto a photosensitive material. As the digital optical printers, there are CRT type, Laser type, LCD type, micromirror type and so forth.
The micromirror type optical printer uses a spatial light modulator constituted of an array of a large number of very small mirrors, called a micromirror array. The micromirror array is arranged in a row or in a matrix, i.e. in a plurality of rows. The micromirrors may tilt each individually to reflect a spot light beam in a variable direction. Exemplars of the micromirror type optical printers are disclosed in Japanese Laid-open Patent Application Nos. 9-164727 and 9-314910. Since the micromirror type optical printer utilizes reflection of mirrors, the attenuation of light is smaller than other types, so the printing light is most efficiently utilized. Of the micromirror type spatial light modulator, there are digital micromirror devices (DMD) and piezo-drive type micromirror device (AMD). The DMD uses electrostatic power to tilt the micromirrors, whereas the AMD uses very small piezoelectric elements to tilt the micromirrors. In the optical printers, each micromirror of the DMD and AMD corresponds to one pixel.
To permit changing the print size, a zoom lens has usually been used as a projection lens, and its magnification is changed according to the print size. For changing the lens magnification of the zoom lens, a mechanical lens driving device, such as a motor, is needed. The mechanical device takes a certain time to change the print size. This is disadvantageous for printing pictures successively in different sizes at a high speed.